Uncountable
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B1 adjective /ʌnˈkaʊntəbəl/

Uncountable

无法计数的; 无穷的
Meaning
too many to be counted; innumerable; infinite in quantity
Example
There are uncountable stars in the night sky.
夜空中有无数的星星。
C1 noun /ˈʌndərˌteɪkər/

undertaker

殡葬员
Meaning
A person whose job is to prepare the dead for burial and arrange funerals.
Example
The undertaker prepared the body for the funeral service.
殡葬员为葬礼服务准备了尸体。
B2 adjective /ʌnˈdʒʌst/

Unjust

不公正的; 错误的
Meaning
not fair or right; morally wrong
Example
The punishment was unjust for such a minor offense.
这个惩罚对于如此轻微的罪行来说是不公正的。
C2 verb /ˈʌndjʊleɪt/

undulate

波动
Meaning
To move with a smooth, wave-like motion.
Example
The snake undulated across the sand.
蛇在沙滩上蜿蜒前行。
C2 adjective /ʌnˈtræməld/

untrammeled

无限自由
Meaning
Not restricted or hampered; free and unrestricted.
Example
She enjoyed untrammeled freedom in her new life abroad.
她在国外的新生活中享受着无限自由。
C2 verb /ʌnˈkloʊð/

unclothe

脱衣; 脱掉衣服
Meaning
to remove clothing from someone or something
Example
The nurse helped unclothe the patient for the examination.
护士帮助病人脱衣进行检查。
C1 noun /ˈʌp.rɔːr/

Uproar

骚动; 喧嚣; 混乱
Meaning
a loud and emotional noise or disturbance; public outcry
Example
The announcement caused an uproar among the students.
公告在学生中引起了骚动。
C2 adjective /ʌnˈtɛmpərd/

untempered

失控的
Meaning
not moderated or softened; lacking proper balance or control
Example
The untempered anger of the crowd caused chaos.
人群的失控愤怒引发了混乱。
C1 adjective /ʌnˈtoʊld/

Untold

不可计数的; 无尽的
Meaning
very great in amount or degree; countless; immeasurable
Example
The earthquake caused untold damage to the city.
地震对城市造成了无法计数的损害。
C2 adjective /ˌʌnpriːpəˈzɛsɪŋ/

unprepossessing

不吸引人
Meaning
not attractive or appealing in appearance
Example
Despite his unprepossessing looks, he was very kind and intelligent.
尽管他的外貌不吸引人，他还是非常友善和聪明。
B2 adjective /ʌnˈskɪld/

Unskilled

无技能的; 无技术的工人
Meaning
lacking technical training or ability; not requiring special skills
Example
Many unskilled workers are looking for training opportunities.
许多没有技能的工人正在寻找培训机会。
C1 adjective /ʌnˈhoʊli/

Unholy

亵渎的; 罪恶的; 亵渎的
Meaning
wicked; sinful; profane
Example
The unholy alliance between the two companies caused public outrage.
这两家公司之间的不圣洁联盟引发了公众愤怒。
C1 adjective /ʌnˈsaɪtli/

unsightly

难看
Meaning
Unpleasant to look at; ugly.
Example
The garbage pile created an unsightly view in the park.
垃圾堆在公园里创造了一个难看的景象。
B2 adjective /ʌnˈrɪəl/

unreal

不真实的
Meaning
not real or not based on reality; exaggerated or imaginary
Example
The experience felt unreal after the sudden news.
突如其来的消息后，这种经历感觉不真实。
C2 adjective /ˌʌnəˈʃʊəd/

unassured

不确定的
Meaning
Lacking confidence or certainty.
Example
She gave an unassured answer during the interview.
她在面试中给出了一个不确定的答案。
C2 verb /ʌnˈfɛtər/

unfetter

解开束缚
Meaning
to release from restraint or restriction; to free
Example
The new law will unfetter small businesses from excessive regulations.
新法律将使小企业免于过多的规定。
B2 adjective /ˌʌnəˈvɔɪdəbəl/

Unavoidable

不可避免的; 无法回避的; 必然的
Meaning
cannot be avoided; certain to happen; inevitable
Example
The meeting is unavoidable, so we must attend.
这个会议是无法避免的，我们必须参加。
C1 adjective /ʌnˈʃeɪkən/

Unshaken

坚定不移; 坚固
Meaning
not disturbed or affected; firm and steady; unwavering
Example
Her faith remained unshaken despite all the challenges.
尽管面临所有挑战，她的信念依然坚定不移。
B2 adjective /ʌnˈlɔːfl/

Unlawful

非法; 不合法
Meaning
not authorized by law; illegal
Example
The court declared the search unlawful.
法院宣布搜索是非法的。
C1 adjective /ʌnˈsəʊʃəbl/

unsociable

不合群的
Meaning
not enjoying the company of others; avoiding social interaction
Example
He became unsociable after moving to a new city.
搬到新城市后，他变得不合群。
C1 noun /ˈʌndərdɒɡ/

underdog

逆袭者
Meaning
a competitor thought to have little chance of winning; a weaker party in a contest
Example
The underdog team surprised everyone by winning the championship.
逆袭者队伍通过赢得锦标赛让所有人都惊讶。
C2 adjective /juːˈbɪkwɪtəs/

ubiquitious

无处不在
Meaning
Present, appearing, or found everywhere.
Example
Smartphones have become ubiquitous in modern society.
智能手机已经在现代社会中无处不在。
B2 adjective /ʌnˈiːkwəl/

Unequal

不平等; 不公正;
Meaning
not the same in quantity, size, or value; not fair or just
Example
The distribution of wealth is unequal in many countries.
财富的分配在许多国家是不平等的。
A2 adjective /ˈʌɡ.li/

Ugly

丑陋的; 可憎的; 可怕的
Meaning
unpleasant or repulsive in appearance; morally reprehensible
Example
The old building looked ugly after years of neglect.
这座老建筑在多年疏忽之后看起来很丑。
A2 noun /ʌmˈbrɛlə/

umbrella

伞
Meaning
A device used for protection against rain or sun, typically consisting of a collapsible canopy mounted on a central rod.
Example
She opened her umbrella as it started to rain.
下雨时她打开了她的伞。
C1 adjective /ʌnˈsteɪtɪd/

unstated

未声明
Meaning
not expressed directly in words; implied or left unsaid
Example
The contract included several unstated expectations.
合同包括了几个未声明的期望。
A2 preposition /əˈpɒn/

upon

之后
Meaning
on or immediately after
Example
Upon hearing the news, he rushed to the hospital.
听到消息后，他赶到医院。
B1 adjective /ʌnˈlaɪkli/

Unlikely

不太可能; 不大可能
Meaning
not likely to happen; improbable
Example
It's unlikely to rain today with such clear skies.
今天晴空万里，几乎不可能下雨。
B1 adjective /ʌnˈkaɪnd/

Unkind

残忍; 不友好
Meaning
cruel; not nice or caring toward others
Example
It was unkind of him to make fun of her appearance.
他取笑她的外貌，真是太不友善了。
B2 adverb /ʌnˈfɛərli/

unfairly

不公平地
Meaning
In a manner that is not just, reasonable, or impartial
Example
He was treated unfairly by the committee.
他被委员会不公平地对待。
C1 adjective /ʌnˈkʌltʃəd/

Uncultured

不文明的; 无文化的
Meaning
lacking good manners, refinement, or education; uncivilized
Example
His uncultured behavior embarrassed everyone at the dinner party.
他在晚宴上的不文明行为让所有人感到尴尬。
C1 adjective /ʌnˈkwaɪ.ət/

Unquiet

不安的; 焦虑的; 激动的
Meaning
restless; unable to remain still or quiet; anxious or troubled
Example
She spent an unquiet night worrying about the exam results.
她度过了一个不安的夜晚，担心考试结果。
A1 pronoun /ʌs/

us

我们
Meaning
used to refer to the speaker and one or more other people as the object of a verb or preposition
Example
She gave us a gift.
她给了我们一个礼物。
C2 adjective /ʌnˈflɛdʒd/

unfledged

未经训练的
Meaning
Inexperienced, immature, or not fully developed.
Example
The unfledged writer struggled to complete his first novel.
这个未经训练的作家难以完成他的第一本小说。
B1 adjective /ˈʌpər/

upper

上层
Meaning
higher in position or rank
Example
The upper floor of the building is under renovation.
建筑物的上层正在翻修。
B2 adjective /ʌnˈprɒf.ɪ.tə.bl̩/

Unprofitable

无利可图
Meaning
not yielding profit or gain; not producing financial benefit
Example
The unprofitable business was forced to close down after three years.
这个无利可图的生意在三年后被迫关闭。
C1 verb /ʌnˈmɑːsk/

unmask

揭露；暴露真相
Meaning
to remove a mask or covering; to reveal the true identity, nature, or intentions of someone or something
Example
The investigation helped unmask the real culprit behind the crime.
调查帮助揭露了犯罪背后的真正罪犯。
B2 adjective /ˌʌndɪˈnaɪəbl/

Undeniable

不容置疑
Meaning
impossible to deny or dispute; clearly true
Example
The evidence of his guilt was undeniable.
他的罪行证据是不容置疑的。
C1 verb /ʌnˈɜːθ/

unearth

发掘
Meaning
To dig up from the ground or to discover something hidden.
Example
Archaeologists unearthed ancient artifacts at the site.
考古学家在遗址发掘了古代文物。
B2 adjective /ˌʌnkənˈtroʊld/

uncontrolled

无法控制的
Meaning
not restrained or managed; lacking control
Example
The wildfire spread in an uncontrolled manner, causing widespread damage.
野火以无法控制的方式蔓延，造成广泛破坏。
C2 noun /ˈjuːzjuːfrʌkt/

usufruct

使用权
Meaning
The legal right to use and enjoy the benefits of someone else’s property without owning it.
Example
The tenant had the usufruct of the land but not its ownership.
租户有权使用这片土地，但没有所有权。
C1 noun /ˈʌndərˌwɜːrld/

underworld

地下世界
Meaning
The criminal world of organized crime or the mythical world of the dead.
Example
The detective spent years studying the secrets of the underworld.
侦探花了很多年研究地下世界的秘密。
C1 adjective /ˌʌndərɪkˈspoʊzd/

underexposed

曝光不足，忽视的
Meaning
insufficiently exposed to light (in photography) or not given enough attention
Example
The photo was underexposed and looked too dark.
照片曝光不足，看起来太暗了。
B2 adjective ʌnˈprɛsɪˌdɛntɪd

unprecedented

前所未有
Meaning
Never done or known before; without previous example.
Example
Unprecedented advancements in science changed human lives.
科学上的前所未有的进展改变了人类的生活。
B1 adjective /ʌnˈedjʊkeɪtɪd/

Uneducated

未受教育的; 文盲
Meaning
lacking education; not having received formal schooling or training
Example
Many uneducated workers struggle to find well-paying jobs.
许多未受教育的工人很难找到薪水高的工作。
A2 conjunction /ʌnˈlɛs/

unless

除非
Meaning
except if
Example
We won't go unless it stops raining.
除非雨停了，否则我们不去。
C1 adjective /ˌʌnɪˈkwɪvəkəl/

unequivocal

明确
Meaning
Leaving no doubt; clear and unambiguous
Example
She gave an unequivocal answer to the question.
她对问题给出了明确的回答。
C1 adjective /ʌnˈkɒm.prə.maɪ.zɪŋ/

Uncompromising

不妥协, 固执
Meaning
unwilling to change one's views or to agree about something; showing an unwillingness to make concessions to others
Example
He was uncompromising in his demand for a full apology.
他在要求完全道歉时非常坚决。
C2 adjective /ʌnˈtʃeɪst/

Unchaste

不道德的; 不纯洁的;
Meaning
not celibate; having engaged in sexual relations; lacking moral purity
Example
The conservative society considered her behavior unchaste and improper.
保守的社会认为她的行为不道德和不合适。
B2 adjective /ʌnˈhɜːd/

Unheard

未听到的; 未知的
Meaning
not heard or listened to; not given a hearing; unknown or unfamiliar
Example
His complaints went unheard by the management.
他的投诉没有被管理层听到。
C2 adjective /ʌnəˈpiːzd/

unappeased

不平息的
Meaning
Not satisfied or calmed; still feeling discontent or anger
Example
Despite the apology, she remained unappeased.
尽管道歉，她仍然不平息的。
C1 verb /ˌʌndərˈvæljuː/

undervalue

低估
Meaning
To assign too low a value or importance to something or someone.
Example
She felt that her boss consistently undervalued her contributions.
她感觉到她的老板总是低估她的贡献。
C1 adjective /ʌnˈweɪ.vər.ɪŋ/

unwavering

坚定
Meaning
Steady or resolute; not wavering.
Example
He showed unwavering dedication to his goal.
他展示了对目标的坚定承诺。
A2 adjective /ˈjuːs.ləs/

Useless

无用
Meaning
having no beneficial purpose; not useful
Example
This broken computer is completely useless.
这个坏掉的电脑完全是无用的。
C1 adjective /ˈʌndərhænd/

underhand

阴险
Meaning
done secretly and dishonestly; deceitful
Example
The politician was accused of using underhand tactics to win the election.
那位政治家被指控使用阴险的手段赢得选举。
C1 adjective /ʌnˈsəʊʃəl/

unsocial

不合群的
Meaning
not enjoying the company of others; avoiding social interaction; contrary to social norms
Example
He prefers unsocial hours so he can work alone without interruptions.
他更喜欢不合群的工作时间来独自工作。
B2 adjective /ˌʌnɪnˈtenʃənəl/

Unintentional

非故意的；意外的
Meaning
not done on purpose; accidental
Example
The damage to the car was unintentional.
车的损坏是非故意的。
A1 preposition /ˈʌndər/

under

下
Meaning
in or to a lower position than something
Example
The cat is under the table.
猫在桌子下面。
B2 verb /ˌʌndərˈteɪk/

undertake

承担
Meaning
to commit to and begin a task or project; to take on responsibility
Example
She decided to undertake a challenging project.
她决定承担一个具有挑战性的项目。
B2 adjective /ʌnˈɪndʒərd/

uninjured

未受伤
Meaning
Without injury; not physically harmed.
Example
All the passengers were rescued uninjured.
所有乘客都没有受伤并被救援。
C1 noun /ˈjuːnɪsən/

unison

齐声
Meaning
Simultaneous performance or utterance of action or speech.
Example
The choir sang in unison.
合唱团齐声唱歌。
B2 adjective /ʌnˈθɪŋkəbl/

Unthinkable

难以想象的
Meaning
impossible to conceive or imagine; beyond belief or consideration
Example
It was unthinkable that such a tragedy could happen in our peaceful town.
在我们和平的小镇上发生这样一场悲剧，简直是难以想象的。
C1 verb /ʌnˈnɜːrv/

unnerve

失去信心
Meaning
to make someone lose confidence, courage, or composure
Example
The hostile questions began to unnerve the witness.
敌对问题开始让证人感到不安。
B1 adverb /ʌnˈfɔːrtʃənətli/

Unfortunately

不幸地
Meaning
used to express regret or disappointment about something
Example
Unfortunately, the weather was bad for our picnic.
很遗憾，天气不适合我们的野餐。
C1 adjective /ˌʌnsəˈfɪstɪˌkeɪtɪd/

unsophisticated

不复杂
Meaning
Lacking worldly experience, refinement, or complexity.
Example
The villagers led an unsophisticated but happy life.
村民过着简单而幸福的生活。
C2 noun /ˈʌmbrɪdʒ/

umbrage

冒犯，愤怒
Meaning
A feeling of resentment or offense.
Example
She took umbrage at his rude remark.
她对他的粗鲁言论感到愤怒。
B2 adjective /ˌʌnəˈveɪləbəl/

unavailable

不可用
Meaning
Not able to be obtained, reached, or used; not present or accessible.
Example
The manager was unavailable to take calls during the meeting.
经理在会议期间不可用，无法接听电话。
C1 adjective /ʌnˈvaɪəbl/

unviable

不可行的
Meaning
Not capable of working successfully; not feasible or practical.
Example
The project was deemed unviable due to high costs.
由于高昂的成本，该项目被认为不可行。
B1 adjective /ˈjuːnɪfɔːrm/

Uniform

制服
Meaning
consistent; identical; standardized
Example
All students must wear a uniform to school.
所有学生必须穿制服上学。
C2 adjective /ˌʌnəˈsweɪdʒd/

unassuaged

未缓解
Meaning
Not made less intense or relieved; unrelieved.
Example
His grief remained unassuaged despite the passage of time.
他的痛苦尽管时间流逝依然未缓解。
B1 adjective /ʌnˈjuzd/

Unused

未使用的; 没有被使用
Meaning
not being used; not having been used before
Example
There are many unused rooms in this old mansion.
这个古老的豪宅里有许多未使用的房间。
C1 noun /ˈʌp.ʃɒt/

Upshot

结果; 结论
Meaning
the final result or outcome of a series of events; conclusion
Example
The upshot of the meeting was a decision to postpone the project.
会议的结果是决定推迟项目。
C1 noun /ʌnɪmˈpɔːrtəns/

unimportance

不重要
Meaning
the state or quality of being insignificant or not important
Example
He dismissed the issue with a sense of unimportance.
他以無關緊要的態度忽略了這個問題。
B2 adjective /ˌʌnprɪˈdɪktəbəl/

unpredictable

不可预测的
Meaning
not able to be predicted; changing suddenly and unexpectedly
Example
The weather in this region is highly unpredictable.
这个地区的天气非常不可预测。
B2 adjective /ʌnfəˈmɪl.jər/

Unfamiliar

不熟悉的; 陌生的
Meaning
not known or recognized; strange
Example
The city was unfamiliar to me since I had never been there before.
这座城市对我来说很陌生，因为我以前从未去过那里。
C2 verb /ʌpˈhiːv/

upheave

抬起
Meaning
to lift or raise something forcefully; to cause to rise suddenly
Example
The workers had to upheave the heavy stone to clear the path.
工人们不得不抬起重石来清理道路。
B1 adjective /ʌnˈmærid/

unmarried

未婚
Meaning
Not married; single.
Example
He is thirty-five and still unmarried.
他三十五岁，仍然未婚。
C1 adjective /ˈʌpərˌmoʊst/

uppermost

最高
Meaning
situated at the highest place or most important
Example
Her family's safety was uppermost in her mind during the crisis.
她在危机期间心里最重要的是家庭的安全。
C1 adjective /ˌʌnəˈkaʊntəbl/

unaccountable

无法解释
Meaning
Not able to be explained or justified.
Example
She felt an unaccountable fear as she entered the dark room.
她进入黑暗的房间时感到无法解释的恐惧。
A2 adjective /ʌnˈkʌmf.tə.bəl/

Uncomfortable

不舒服
Meaning
causing or feeling slight pain or physical discomfort; making someone feel embarrassed, awkward, or anxious
Example
The chair was so uncomfortable that I couldn't sit in it for more than ten minutes.
这个椅子太不舒服了，我坐在上面超过十分钟就坐不下来了。
B1 adjective /ʌnˈfeər/

Unfair

不公平; 不正当;
Meaning
not right or just; treating people in a way that favors some over others
Example
It's unfair to blame her for something she didn't do.
指责她做了她没有做的事是不公平的。
C1 adjective /ˌʌnbɪˈliːvɪŋ/

unbelieving

不相信的
Meaning
Not willing or able to believe; skeptical or doubtful
Example
She gave him an unbelieving look when he claimed to have met a celebrity.
当他声称见过一位名人时，她给了他一个不相信的眼神。
A1 adjective /ˈjuːs.fəl/

Useful

有用的; 实用的
Meaning
having a beneficial purpose; practical
Example
This tool is very useful for fixing problems.
这个工具对解决问题非常有用。
C2 adjective /juːˈʒʊəriəs/

usurious

高利贷的
Meaning
Charging excessively high interest rates on loans.
Example
The bank was accused of offering loans at usurious rates.
该银行被指控以高利贷利率提供贷款。
B2 adjective /ʌnˈfɪt/

Unfit

不适合; 不适当;
Meaning
not in good physical condition; unsuitable or inappropriate
Example
He was declared unfit for military service due to his poor health.
由于健康状况差，他被宣判不适合军事服务。
C2 adjective /ʌpˈrɔːr.i.əs/

uproarious

极其滑稽
Meaning
Extremely funny or noisy; causing loud laughter or commotion.
Example
The comedian's jokes were absolutely uproarious.
喜剧演员的笑话绝对是极其滑稽的。
C2 adjective /ʌnˈspɛərɪŋ/

unsparing

无情的
Meaning
Showing no mercy or generosity; harsh or severe.
Example
The critic was unsparing in his review of the play.
评论家在他的剧评中毫不留情。
C2 adjective /ʌnˈsʌlid/

unsullied

无暇
Meaning
not spoiled or made impure; perfectly clean or pure
Example
His reputation remained unsullied despite the accusations.
尽管有指控，他的声誉仍然无暇。
C1 adjective ʌnˈjiːl.dɪŋ

unyielding

坚定或坚韧
Meaning
Not easily broken or giving in to pressure.
Example
Her unyielding determination helped her overcome all challenges.
她坚定的决心帮助她克服了所有的挑战。
B2 adverb /ʌnˈdaʊtɪdli/

undoubtedly

毫无疑问
Meaning
without a doubt, certainly
Example
He is undoubtedly the best player on the team.
他毫无疑问是队里最好的球员。
B2 adjective /ʌnˈtʃeɪndʒɪŋ/

unchanging

不变的
Meaning
remaining the same over time; not changing
Example
Her love for her family was unchanging throughout the years.
她对家人的爱多年来始终不变。
B1 verb /ˈʌpˌɡreɪd/

upgrade

升级
Meaning
to raise something to a higher standard, improve
Example
We decided to upgrade the software to the latest version.
我们决定将软件升级到最新版本。
C1 adjective /ˌʌn.əˈdʌl.tə.reɪ.tɪd/

Unadulterated

纯净的
Meaning
not mixed or diluted with any different or extra elements; pure
Example
She felt unadulterated joy when she heard the news.
当她听到这个消息时，她感到纯净的快乐。
C2 noun /ˈʌŋɡwənt/

unguent

药膏
Meaning
A soothing or healing ointment applied to the skin.
Example
The doctor applied an unguent to heal the burn.
医生涂抹了药膏来治愈烧伤。
B2 adjective /ʌnˈtʃeɪndʒəbəl/

Unchangeable

不可改变的; 固定的;
Meaning
not able to be changed or altered; fixed and permanent
Example
The laws of physics are unchangeable principles that govern the universe.
物理法则是不变的原则，支配着宇宙。
B1 adjective /ʌnˈseɪf/

Unsafe

不安全; 危险的;
Meaning
involving or causing danger or risk; not protected from harm
Example
It is unsafe to walk alone in this neighborhood at night.
晚上在这个社区独自行走是不安全的。
B2 adverb /ʌnˈkɒnʃəsli/

unconsciously

无意识地
Meaning
without being aware of one's actions or surroundings
Example
She unconsciously tapped her foot to the rhythm of the music.
她无意识地跟着音乐的节奏轻轻跺脚。
C1 adjective /ʌnˈdɔːntɪd/

Undaunted

无畏的; 勇敢的; 不屈的;
Meaning
not intimidated or discouraged by difficulty, danger, or disappointment
Example
Despite the setbacks, she remained undaunted in pursuing her goals.
尽管遇到挫折，她在追求目标时依然无畏。
B2 verb /ʌnˈkʌvə(r)/

uncover

揭示
Meaning
to reveal something that was hidden or secret
Example
The investigation uncovered new evidence.
调查揭示了新的证据。
B1 adjective /ʌnˈklɪər/

unclear

不清楚
Meaning
not easy to understand; vague or ambiguous
Example
The instructions were unclear, so I asked for clarification.
说明不清楚，所以我要求澄清。
C2 noun juːˈbɪkwɪti

ubiquity

普遍性
Meaning
The fact of appearing everywhere or of being very common.
Example
The ubiquity of smartphones has transformed communication.
智能手机的普遍性改变了通信方式。
C1 noun /ˈʌndərˌstʌdi/

understudy

替身演员
Meaning
An actor who learns another's role to act as a replacement if needed.
Example
The understudy performed when the lead actor fell ill.
当主角生病时，替身演员上场表演。
B2 adjective /ˈʌt.moʊst/

Utmost

最极; 极限
Meaning
greatest; most extreme; maximum possible
Example
She showed utmost care while handling the fragile items.
她在处理脆弱物品时表现出最大的关心。
B1 adjective /ˌʌnsəkˈsesfl/

Unsuccessful

失败的; 没有成功的;
Meaning
not achieving desired aims or results; failing to accomplish a purpose
Example
His unsuccessful attempt to climb the mountain left him disappointed.
他未能成功登上山顶，感到失望。
C2 adjective /ʌnˈblʌʃɪŋ/

Unblushing

厚颜无耻的; 放肆的
Meaning
showing no shame or embarrassment; boldly shameless
Example
He told the unblushing lie without any hesitation.
他毫不犹豫地说了那个无耻的谎言。
B2 verb /ˌʌndərˈmaɪn/

undermine

削弱
Meaning
to gradually weaken or damage something or someone
Example
Constant criticism can undermine a child's confidence.
持续的批评可能会削弱孩子的自信心。
C2 noun /ˈʌm.brə/

Umbra

完全的阴影，太阳黑子的黑暗中心
Meaning
the fully shaded inner region of a shadow cast by an opaque object; the dark center of a sunspot
Example
During the eclipse, we stood in the moon's umbra.
在日食期间，我们站在月亮的本影中。
C2 adjective /ʌnˈælɔɪd/

unalloyed

纯净
Meaning
Pure, complete, and not mixed with anything else.
Example
She felt unalloyed joy at the news of her success.
她听到成功的消息时感到纯粹的喜悦。
B2 noun /ˌʌnəˌveɪləˈbɪləti/

unavailability

不可用性
Meaning
The state of being not available or not accessible.
Example
The unavailability of the manager caused a delay in the project.
经理的不可用性导致了项目的延误。
B2 adjective /ʌnˈwɜːrði/

Unworthy

不配; 没有价值
Meaning
not deserving respect or attention; lacking worth or merit
Example
He felt unworthy of such praise and recognition.
他觉得自己不配得到这样的赞扬和认可。
B2 verb /ʌnˈtaɪ/

untie

解开
Meaning
to loosen or remove a knot or binding; to release something that is tied
Example
She untied the rope to free the boat.
她解开绳子来释放船只。
B2 adverb /ʌnˈsɜːrtənli/

uncertainly

不确定地
Meaning
in a way that shows doubt or lack of certainty
Example
She glanced uncertainly at the complicated instructions.
她不确定地看着复杂的说明。
B1 adjective /ˌʌnˈɪntrəstɪŋ/

uninteresting

无趣的
Meaning
not holding attention or curiosity; boring
Example
The lecture was uninteresting and difficult to stay focused on.
这次讲座很无趣，很难集中注意力。
C2 verb /ˌʌndərˈɡɜːrd/

undergird

支持，强化
Meaning
to provide support or foundation for; to strengthen
Example
Strong values undergird a healthy society.
强大的价值观支撑着一个健康的社会。
C1 adjective /ʌlˈtɪəriər/

ulterior

隐藏的动机
Meaning
hidden or secret, often with a selfish motive
Example
He invited her with an ulterior motive.
他带着隐藏的动机邀请了她。
C2 noun /juːˌtɪlɪˈtɛəriənɪzəm/

utilitarianism

功利主义
Meaning
The ethical theory that actions are right if they are useful or for the benefit of the majority.
Example
Utilitarianism suggests that we should act to maximize overall happiness.
功利主义认为我们应该采取行动，以最大化整体幸福。
B2 adverb /ʌnˈplɛzəntli/

unpleasantly

令人不快地
Meaning
in a way that causes discomfort, annoyance, or displeasure; in an unfriendly or disagreeable manner
Example
The room was unpleasantly hot during the afternoon.
下午房间里热得令人不快。
C1 adjective /ʌnˈseɪvəri/

unsavory

令人不快
Meaning
Disagreeable, unpleasant, or morally offensive.
Example
The politician was linked to an unsavory scandal.
那位政治家与一宗令人不快的丑闻有关。
B2 adjective /ʌnˈriːzənəbəl/

unreasonable

不合理的
Meaning
not guided by reason or fairness; excessive or extreme beyond what is acceptable
Example
The manager made an unreasonable demand that no one could realistically meet.
经理提出了一个不合理的要求。
C2 adjective /ʌnˈwəʊntɪd/

unwonted

不寻常
Meaning
Unusual, uncommon, or out of the ordinary.
Example
She spoke with an unwonted gentleness that surprised everyone.
她以一种不寻常的温柔说话，令所有人都感到惊讶。
B1 adjective /ʌnˈkʊkt/

uncooked

生的
Meaning
Not cooked; in a raw state.
Example
Eating uncooked meat can be dangerous.
吃生肉可能是危险的。